Transport of cerium oxide nanoparticles in saturated silica media: influences of operational parameters and aqueous chemical conditions

Abstract

This paper aimed to investigate the influences of operational parameters and aqueous chemical conditions on transport behaviors of cerium oxides nanoparticles (CeO₂-NPs) in saturated silica media. Results indicated that increasing rates of attachment efficiency (α) were related with cationic types, and critical deposition concentration (CDC) for divalent cation (Ca²⁺ and Mg²⁺) were more than 31-fold of that for monovalent cation (Na⁺ and K⁺). Increase or reduction of electrolyte pH could both promote the mobility of CeO₂-NPs in glass beads, while influence was more evident at alkaline conditions. α increased linearly with NPs concentrations, while decreased linearly with flow velocity in the column, and effects were related with electrolyte contents. Presence of surfactants could sharply decreased α, and SDS was more effective to facilitate CeO₂-NPs transport than Triton X-100. With DOMs concentrations increasing, α firstly kept constant, then sharply declined, and finally reduced very slowly. The influence of DOMs on NPs deposition was in order of SA > HA > TA > BSA. Overall, this study revealed that aqueous chemical conditions was crucial to NPs transport in porous media, and would provide significant information for our understanding on the fate and transport of nanoparticles in natural environment.

Figure 1

Illustrative transport results and critical deposition curves of CeO₂-NPs at varying NaCl concentration (a) and four different cationic solutions (b). (a) Were normalized column effluent NPs concentrations versus number of pore volumes for washing solution at pH of 5.54. (b) were obtained at pH 5.54, injection of 1 mL 100 mg/L NPs, and flow rate of 2.0 mL/min.

Figure 2. The critical deposition curves of CeO₂-NPs at pH of 4, 5.54 and 10 with NaCl as the electrolyte.

100 mg/L CeO₂-NPs was pulsing injected into the transport column at 1 mL.

Figure 3. Attachment efficiency and deposition rate of CeO₂-NPs for different nanoparticle concentrations (10–200 mg/L) in NaCl and CaCl₂ at the flow rate of 2.0 mL/min.

(a) α changed with CeO₂-NPs conentration with NaCl of 10 and 50 mM as electrolyte; (b) α changed with CeO₂-NPs conentration with CaCl₂ of 0.25 and 0.8 mM as electrolyte; (c) k_d changed with CeO₂-NPs conentration with NaCl and CaCl₂ as electrolyte.

Figure 4. Attachment efficiency of CeO₂-NPs at eight different flow rates (0.5–4.0 mL/min).

Results were obtained at pH of 5.54, injection of 1 mL 100 mg/L NPs, with 20 mM NaCl and 0.5 mM CaCl₂ as electrolyte.

Figure 5. Influence of two surfactants (a) and four DOMs (b) on CeO₂-NPs transport in glass beads columns.

Conditions (a): 1 mL/min 100 mM NaCl + 1 mL/min surfactant solution, injection of 100 mg/L CeO₂ 1 mL, with pore volume 3.22 mL. Conditions (b): 1 mL/min 50 mM NaCl + 1 mL/min organic solution, injection of 100 mg/L CeO₂ 1 mL, with pore volume 3.22 mL.

Figure 6

Critical deposition curves of CeO₂-NPs with varied BSA (a,b) and HA (c,d) concentrations at pH 5.54 in presence of NaCl (a,c) and CaCl₂ (b,d) as background electrolytes. The BSA concentration was selected at 5 and 20 mg/L, while HA concentration was selected at 0.5 and 2.5 mg/L.

Figure 7. Experimental set-up for column transport experiments.